Fuel cell collector plates containing grafted polyolefins

ABSTRACT

A conductive composition for fuel cell collector plates and the molding methods thereof are provided. The molding composition includes a polymer resin and conductive fillers, wherein the polymer resin is a polymer blend comprising (1) from about 10 to 100 wt %, preferably from about 50 to about 100 wt % of a grafted polyolefin or a blend of grafted polyolefins and (2) from 0 to about 90 wt %, preferably from about 0 to about 50 wt % of at least one other thermoplastic polymer having a melting point below 280° C. One type of or a combination of different types of highly conductive fillers are selected from carbon, graphite, metallic fillers and mixtures thereof. The polymer resin and conductive fillers are blended into a homogeneous mixture and molded into a collector plate. A preferred method of injection molding and a preferred method of injection-compression molding are provided to mold the composition into the shape of a fuel cell collector plate having a volume resistivity of not more than about 0.1 ohm.cm. The collector plate is particularly suitable for, but not limited to, use in polymer electrolyte membrane fuel cells.

FIELD OF THE INVENTION

This invention relates to conductive flow field separator plates forfuel cells, and to methods for making such plates. The plates comprise amixture of a polymer resin and conductive fillers, wherein the polymerresin is selected from a grafted polyolefin, a blend of graftedpolyolefins and a blend of a grafted polyolefin and at least one otherthermoplastic polymer having a melting point below 280° C.

BACKGROUND OF THE INVENTION

With the fast rising global demand for cheap and clean power, thedevelopment of polymer electrolyte membrane fuel cells has acceleratedgreatly. A typical single solid polymer electrolyte membrane fuel cellof the prior art is shown in FIG. 1. The fuel cell comprises an anodecurrent collector plate 1, an anode-backing layer 2, an anode catalystlayer 3, a polymer electrolyte membrane 4, a cathode catalyst layer 5, acathode-backing layer 6 and a cathode current collector plate 7.Individual fuel cells may be connected in series to form a fuel cellstack.

Current collector plates, also called flow field plates or separatorplates, perform the functions of connecting individual cells, collectingcell current generated within the cells, accommodating or distributingcell reactants, removing cell reaction products and assisting withthermal control. To meet these requirements, the collector, plates musthave excellent electrical conductivity, good mechanical strength,sufficient chemical stability and low gas permeability. As well, thematerials used to make the plates, and their method of manufacture, musthave a low cost to allow the plates to be commercially viable.

A typical collector plate requires flow field channels 8, 9 in FIG. 1 onits surfaces to direct fuel reactants or oxygen, and reactionby-products such as water. Graphite plates with machined flow fieldshave historically been used as collector plates for fuel cells. Due totheir brittleness and high fabrication/machining cost, graphite platesare relatively expensive to make such that they cannot meet therequirements for large-scale commercialization of fuel cells.

Recently, substantial efforts have been focused on making collectorplates by molding of thermoplastic conductive polymer compositions.These plates can have flow-field channels molded directly onto theirsurfaces without having to post-machine the flow fields. Some of theseefforts are described in published PCT patent application nos.WO99/49530, WO00/30202, WO00/30203 and WO00/44005. Polyphenylene ether,polyphenylene sulfide, modified polyphenylene oxide, and liquid crystalpolymer have been used as the preferred resins for making the collectorplates by molding. These compositions, however, can have significantdisadvantages, including:

-   -   a. All these resins are very expensive. Their use therefore        results in higher costs for collector plates and fuel cell        units.    -   b. All these resins require high melt processing temperature        (above 280° C.) and high mold temperature (above 100° C.) during        the manufacturing process of the collector plates. A very long        heating/cooling cycle, high energy consumption and high        machinery cost become the major hurdles for cost reduction in        the commercial manufacturing process of these collector plates.

U.S. Pat. No. 6,511,768 discloses the use of a polypropylene-basedconductive porous matrix for fabricating electrode materials. U.S. Pat.No. 5,804,116 discloses plates comprising polypropylene that have goodthermal conductivity, but no mention is made of their electricalconductivity.

Thus, there is a need for developing a relatively low cost and highlyconductive composition that has low melt viscosity or good moldabilityand can be easily processed below a temperature of 280° C. and issuitable for application as fuel cell collector plates.

It is therefore one aspect of the present invention to provide a lowcost and highly conductive polymer composition comprising an inexpensivepolymer material and conductive fillers. The composition preferably haslow melt viscosity, good moldability and provides excellent electricalconductivity and sufficient mechanical strength after being molded intocollector plates for use in fuel cells.

It is another aspect of the present invention to provide a method ofpreparing the composition and of molding the composition into collectorplates using a fast molding process.

The disclosures of all patents/applications referenced herein areincorporated herein by reference.

SUMMARY OF THE INVENTION

In accordance with one aspect of the present invention, there isprovided an electrically conductive shaped article comprising a polymerresin and conductive fillers, wherein the polymer resin is a polymerblend comprising (1) from about 10 to 100 wt %, preferably from about 50to about 100 wt % of a grafted polyolefin or a blend of graftedpolyolefins and (2) from 0 to about 90 wt %, preferably from about 0 toabout 50 wt % of at least one other thermoplastic polymer having amelting point below 280° C.

In accordance with a second aspect of the present invention, there isprovided a conductive flow field separator plate for use in a polymerelectrolyte membrane fuel cell comprising a polymer resin and conductivefillers, wherein the polymer resin is a polymer blend comprising (1)from about 10 to 100 wt %, preferably from about 50 to about 100 wt % ofa grafted polyolefin or a blend of grafted polyolefins and (2) from 0 toabout 90 wt %, preferably from about 0 to about 50 wt % of at least oneother thermoplastic polymer having a melting point below 280° C.

In accordance with a further aspect of the present invention, there isprovided a method of making a conductive flow field separator platecomprising the steps of:

-   -   (a) mixing a polymer resin with conductive fillers to form a        conductive blend, wherein the polymer resin is a polymer blend        comprising (1) from about 10 to 100 wt %, preferably from about        50 to about 100 wt % of a grafted polyolefin or a blend of        grafted polyolefins and (2) from 0 to about 90 wt %, preferably        from about 0 to about 50 wt % of at least one other        thermoplastic polymer having a melting point below 280° C.; and    -   (b) molding the conductive blend to form the conductive flow        field separator plate.

In yet a further aspect of the present invention, there is provided aprocess for making a conductive flow field separator plate for use inpolymer electrolyte membrane fuel cells comprising the steps of:

-   -   (a) feeding a mixture of a polymer resin and conductive fillers        into an injection molding machine, wherein the polymer resin is        a polymer blend comprising (1) from about 10 to 100 wt %,        preferably from about 50 to about 100 wt % of a grafted        polyolefin or a blend of grafted polyolefins and (2) from 0 to        about 90 wt %, preferably from about 0 to about 50 wt % of at        least one other thermoplastic polymer having a melting point        below 280° C.,    -   (b) plasticising the mixture at a temperature above the melting        point of the polymer resin to form a melt,    -   (c) injecting the melt into a mold,    -   (d) allowing the melt to cure in the mold to form the conductive        flow field separator plate, and    -   (e) removing the conductive flow field separator plate from the        mold.

In preferred embodiments, the present invention relates to a conductivecomposition comprising from about 10 to about 50 wt %, preferably fromabout 15 to about 25 wt % of the polymer resin and from about 50 toabout 90 wt %, preferably from about 75 to about 85 wt % of one type ora combination of different types of conductive fillers selected fromcarbon fillers, graphite fillers, metal fillers, inherently conductivepolymers, and mixtures thereof.

The preferred conductive composition of the present invention may bemolded to form a fuel cell collector plate by compression molding,injection molding, or injection-compression molding, extrusion, transfermolding, extrusion-transfer-pressing, calendering, laminating, coatingor by other suitable molding methods. Preferably, the preferredconductive composition of the present invention is molded by injectionmolding or injection-compression molding to form a fuel cell collectorplate. The molded fuel cell collector plate made from the preferredconductive composition has a volume resistivity (Four Point method) ofnot more than about 0.1 ohm.cm and a flexural strength of not less thanabout 3000 Psi. The molded plates are particularly suitable for use ascurrent collector plates in solid polymer electrolyte fuel cells.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will be described with reference tothe accompanying drawings in which like numerals refer to the same partsin the several views and in which:

FIG. 1: is a schematic perspective view of a typical fuel cell of theprior art.

FIG. 2: is a flow chart showing the steps in a preferred embodiment ofthe method of manufacturing separator plates of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments of the present invention will now be describedwith reference to the accompanying figures.

With reference to FIG. 1, there is shown in a schematic perspectiveview, a typical fuel cell of the prior art. This typical polymerelectrolyte membrane fuel cell includes an anode current collector plate(1), an anode backing layer (2), an anode catalyst layer (3), a membrane(4), a cathode catalyst layer (5), a cathode backing layer (6), acathode current collector plate (7), and plate flow field channels (8)and (9).

Generally, the present invention relates to a conductive composition formaking current collector plates (1) and (7). Briefly, in the preferredembodiment, the conductive composition comprises a mixture of a polymerresin and conductive fillers. The total amount of the polymer resin inthe composition is from about 10 to about 50 wt %, preferably from about15 to about 25 wt %, while the total amount of the conductive fillers inthe composition is from about 50 to about 90 wt %, preferably from about15 to about 25 wt %, based on the total weight of the polymerresin/filler mixture. The polymer resin/filler mixture is mixed orcompounded into a homogeneous mixture and subsequently fed into amolding machine to mold a current collector plate. The polymerresin/filler mixture is preferably prepared by dry-blending the polymerresin/filler mixture in a blender or a container at a temperature belowthe melting point of the polymer resin. The polymer resin/filler mixtureis then fed directly into a molding machine, such as an injectionmolding machine or an injection-compression molding machine to mold acurrent collector plate having a volume resistivity of not more than 0.1ohm.cm and a flexural strength of higher than about 3000 Psi.

The polymer resin useful in the present invention is a graftedpolyolefin, a blend of grafted polyolefins or a polymer blend comprising(1) from about 10 to 100 wt %, preferably from about 50 to about 100 wt% of a grafted polyolefin or a blend of grafted polyolefins and (2) from0 to about 90 wt %, preferably from about 0 to about 50 wt % of at leastone other thermoplastic polymer having a melting point below 280° C.

Preferably, the grafted polyolefin is a low cost polymer material withhigh melt flow rate, such as maleic anhydride grafted polypropylene. Thegrafted polyolefin can be manufactured by different processes such asmelt grafting, solution grafting and radiation grafting processes.Examples of grafting processes are described in GB2081723, U.S. Pat. No.4,298,712, WO94/25498 and WO95/24449, all of which are incorporatedherein by reference. The grafted polyolefins suitable for the presentinvention include grafted homopolymers and copolymers of unsaturatedhydrocarbons having 2-20 carbon atoms. They can also be made byprocesses well known in the art, including polymerization processes inwhich metallocene catalysts are used (single site catalysts). Forexample, the polymers are homopolymers of ethylene or propylene orcopolymers of ethylene with one or more alpha-olefin hydrocarbons having3-10 carbon atoms, especially propylene, butene-1, hexene-1 and octene-1and styrene. Suitable alpha-olefins also include dienes, that is,monomers with more than 1 site of unsaturation, especially 1,3butadiene, 1,5 hexadiene, 5-ethylidene-2-norbornene and norbornadiene.In particularly preferred embodiments, the polyolefins are polypropylenehomopolymers and ethylene-propylene copolymers, propylene-alpha olefincopolymers having a density in the range of about 0.850 to about 0.970grams per cubic centimetre (g/cm³) and especially in the range of 0.860to 0.930 g/cm³.

Still other suitable grafted polyolefins that may be used in the presentinvention may be ethylene/alpha olefin copolymers such as copolymers ofethylene and a vinyl alkanoate, especially ethylene/vinyl acetatecopolymers. The copolymers may have a relatively high ethylene content,or lower ethylene contents. In addition, the copolymers are available ina variety of molecular weights, which is usually expressed in terms ofmelt index.

The grafting monomer is preferably selected from the group consisting ofethylenically unsaturated carboxylic acids and ethylenically unsaturatedcarboxylic acid anhydrides, including derivatives of such acids, andmixtures thereof. Examples of the acids and anhydrides, which may bemono-, di- or polycarboxylic acids, are acrylic acid, methacrylic acid,maleic acid, fumaric acid, itaconic acid, crotonic acid, itaconicanhydride, maleic anhydride and substituted maleic anhydride e.g.dimethyl maleic anhydride or citraconic anhydride, nadic anhydride,nadic methyl anhydride and tetrahydro phthalic anhydride. Most suitableethylenically unsaturated acids or acid derivatives include for examplemaleic anhydride, acrylic acid, methacrylic acid and its derivatives.

The weight percentage of the monomers grafted onto the polyolefin ispreferably in the range of about 0.05 wt % to about 10 wt % based on thetotal resin weight. The grafted polyolefin preferably has a melt flowrate (MFR) in the range of about 0.5 to about 1000 g/10 min (teststandard of ASTM D-1238) and most preferably in the range of about 50 to500 g/10 min. The melting point of the grafted polyolefin is preferablyin the range of about 100 to about 280° C. (ASTM D-3418) and mostpreferably in the range of about 140-220° C.

The polymer resin used in the present invention can also be a blend ofthe above-mentioned grafted polyolefins, or a blend of the abovementioned grafted polyolefins and at least one other thermoplasticpolymer having a melting point below 280° C. Examples of suitablethermoplastic polymers include polypropylene, polyethylene, modifiedpolypropylene, modified polyethylene, nylons, polyesters, polycarbonate,polyurethane, acrylonitrile-butadiene-styrene (ABS) etc.

The conductive fillers useful with the present invention may include oneor more conductive fillers selected from the following: carbon fillers,graphite fillers, metal fillers, inherently conductive polymers and amixture thereof. The conductive fillers may be in the shape of sphericalor irregular particles, fibers or flakes. The conductive filler particlesize may be between about 10 and about 500 μm, and the carbon orgraphite fibers preferably have a diameter of less than 15 μm and alength of less than about 10 mm.

The preferred conductive composition of the present invention comprisesfrom about 10 wt % to about 50 wt %, preferably from about 15 wt % toabout 25 wt %, of the polymer resin, and from about 50 wt % to about 90wt %, preferably from about 75 wt % to about 85 wt %, of one type or acombination of different types of the conductive fillers.

The conductive composition of the present invention is suitable forfabricating electrically conductive shaped articles such as currentcollector plates used in fuel cells. These articles may be made usingcompression molding, injection molding or injection-compression molding,extrusion, transfer molding, extrusion-transfer-pressing, calendering,laminating, coating or by other suitable molding methods. A currentcollector plate made in accordance with the present invention may haveflat surfaces or grooves on one or both of its surfaces, wherein thegrooves define a flow-field pattern. The current collector platepreferably has a thickness ranging from about 0.5 mm to about 5 mm and avolume resistivity of not more than about 0.1 ohm.cm. The flexuralstrength of the current collector plates is preferably not less thanabout 3000 Psi.

The volume resistivity is measured using the standard four-point method,which is performed in accordance with the method described in Wieder,HH, Laboratory Notes on Electrical and Galvanomagnetic Measurements,Material Science Monograph, Vol. 2, Elsevier Pub., Amsterdam, 1979,which is herein incorporated by reference. A current (I) is injected atthe first of four linear equispaced point electrode probes and collectedat the fourth electrode, while the potential difference (ΔV) between thesecond and third electrodes is measured. The resistivity (ρ) isdetermined using the following equation where T is the thickness of thesample, and R is the measured resistance.ρ=4.53 RTThe flexural strength of the plates is measured according to ASTM D-790.

As illustrated in FIG. 2, the preferred method for making the currentcollector plates includes two different routes with the following steps.The polymer resin/fillers blend is prepared by dry-blending (tumbling ina container or mixing in a blender) at a temperature below the meltingpoint of the resin. The polymer resin and fillers can be either both inpowder form (Route 1) or both in pellet form (Route 2) in order to bewell mixed in the composition. The polymer resin/fillers blend is thenfed into the hopper of an injection molding machine or aninjection-compression molding machine. The machine barrel has atemperature profile above the melting temperature of the resin. Theblend is plasticized inside the machine barrel and injected into a mold.The molded article is solidified in the mold and removed aftersolidification.

In the case of injection-compression molding, the mold remains half openas the melt is injected into the mold cavity. Subsequently after thisinjection step, the mold is completely closed and compressed(compression step). A gap between the two mold halves helps reduce meltpressure drop and therefore necessitates lower injection pressure fromthe machine injection unit. In some cases, an injection molding machineor an injection-compression molding machine has one hopper for feedingthe resin and another hopper for feeding the fillers, so that the resinand fillers can be fed separately. The fillers hopper is normallylocated on the barrel zone and thus fed at a point after the resin hasbeen melted inside the barrel. This arrangement is preferred as it helpsto reduce serious fiber breakage when conductive fibers are used.

Although in a preferred embodiment, the present conductive compositionis molded into a current collector plate, the composition of the presentinvention may also be used for coating or laminating metallic plates.

The preferred conductive flow field separator plates of the presentinvention are useful for low temperature fuel cell applications and alsofor direct methanol fuel cell applications.

The following examples illustrate the various advantages of thepreferred method of the present invention.

EXAMPLES Example 1

400 grams of maleic anhydride grafted polypropylene powder with anaverage particle size of 500 μm (FUSABOND®, P series, grade M-613-05,maleic anhydride grafting level=0.5 wt %, MFR=120 g/10 min, availablefrom DuPont Canada) and 1600 grams of graphite powder (THBERMOCARB®,grade CF-300, average particle size about 300 μm, available from CONOCO,USA) were dry-blended by tumbling mixing to form a homogeneous blendcomprising 20 wt % of maleic anhydride grafted polypropylene resin and80 wt % of the graphite filler. The mixture was injection molded intocurrent collector plates using a 180 ton NISSEI injection moldingmachine (type FS180S36ASE, NISSEI, Japan) with the following processingconditions:

Screw D=56 mm, and nozzle D=5 mm.

-   -   Mold: 2 cavity plate mold with a fan gate, one 4″×4″× 1/10″ flat        plate and    -   one 4″×4″× 1/10″ grooved plate.    -   Barrel temperature=150, 190, 200, 200° C.    -   Melt temperature=205° C.    -   Mold temperature=80° C.    -   Injection pressure=1354 kg/cm²    -   Back pressure=0 kg/cm²    -   Injection speed=11 cm/s    -   Screw speed=100 rpm

Under these molding conditions, both the flat plate mold and the groovedplate mold were completely filled. The molded plates were well packedwithout short filling problems. The average volume resistivity (usingthe Four Probe Method described above) of the plates was measured as0.06 ohm.cm. The average flexural strength of the plates was measured as4700 psi.

Example 2

500 grams of the same maleic anhydride grafted polypropylene resin asused in Example 1, 200 grams of the same graphite powder as used inExample 1 and 1300 grams of pitch-based graphite fiber (DIALEAD® K223HG,6 mm long pellet, available from Mitsubishi Chemical of America) weredry blended by tumbling mixing to form a homogeneous blend comprising 25wt % of the maleic anhydride grafted polypropylene resin, 10 wt % of thegraphite powder and 65 wt % of the graphite fiber. The blend wasinjection molded on the same machine under the same conditions as usedin Example 1.

Under these molding conditions, both the flat plate mold and the groovedplate mold were completely filled. The molded plates were well packedwithout short filling problems. The average volume resistivity of theplates was measured as 0.1 ohm.cm. The average flexural strength ismeasured as 6004 psi.

Example 3

400 grams of the same maleic anhydride grafted polypropylene as inExample 1, but in pellet form, and 1600 grams of pitch-based graphitefiber as used in Example 2 were dry blended by tumbling mixing to form ahomogeneous mixture comprising 20 wt % of maleic anhydride graftedpolypropylene resin, and 80 wt % of graphite fiber. The mixture wasinjection molded on the same machine under the same molding conditionsas used in Example 1 except that a mold temperature of 120° C. was usedin this example.

Under these molding conditions, both the flat plate mold and the-groovedplate mold were completely filled. The molded plates were well packedwithout short filling problems. The average volume resistivity of theplates was measured as 0.05 ohm.cm. The average flexural strength wasmeasured as 3426 psi.

Example 4

400 grams of the same maleic anhydride grafted polypropylene as used inExample 1 and 1600 grams of graphite powder (THERMOCARB®, fine grade,average particle size 50 μm, available from CONOCO, USA) were dryblended by tumbling mixing to form a homogeneous blend comprising 20 wt% of maleic anhydride grafted polypropylene resin and 80 wt % of thegraphite filler. The mixture was injection molded on a 100 ton SUMITOMO®injection-compression molding machine (SH100C360, SUMITIMO, Japan) withthe following processing conditions:

Screw D=36 mm, nozzle D=5 mm.

-   -   Mold: Central gated disc mold, D=15 cm, Disc thickness with        gradual decrease from 3 mm in center to 1.5 mm at edge    -   Barrel temperature=160, 190, 200, 200° C.    -   Melt temperature=200° C.    -   Mold temperature=80° C.    -   Injection pressure=1100 kg/cm²    -   Back pressure=0 kg/cm²    -   Injection speed=7.5 cm/s    -   Screw speed=80 rpm    -   Compression distance=500 μm.

Under these molding conditions, the plate mold was completely filled andthe molded pates were well packed without short filling problems. Theaverage volume resistivity of the plates was measured as 0.06 ohm.cm.The average flexural strength was measured as 4810 psi.

Comparative Example A

400 grams of ground polypropylene homopolymer resin (AMOCO® 1246, MFR=20g/10 min, average particle size of 500 μm) and 1600 grams of the samegraphite powder as used in Example 1 were dry blended by tumbling mixingto form a homogeneous blend comprising 20 wt % of the polypropyleneresin and 80 wt % of the graphite filler. The blend was injection moldedinto collector plates under same conditions as used in Example 1.

Under these conditions, the flat plate was reluctantly filled withserious melt flow difficulty. The plate mold with grooves was justpartially filled even when using a maximal injection pressure of 1368kg/cm². The average volume resistivity of the plates was measured as0.13 ohm.cm. The average flexural strength was measured as 3353 psi.

Comparative Example 2

300 grams of ground polypropylene homopolymer resin (NOVOLEN®, MFR=120g/10 min, average particle size of 500 μm) and 1200 grams of the samegraphite powder as used in Example 1 were dry blended by tumbling mixingto form a homogeneous blend comprising 20 wt % of the polypropyleneresin and 80 wt % of the graphite filler. The blend was injection moldedinto collector plates under the same conditions used in Example 1.

With these conditions, neither the flat plate nor the grooved one wasfilled due to serious melt flow difficulty. The volume resistivity ofthe plates was measured as 0.2 ohm.cm. There was no sufficient samplesize available for flexural strength test.

Although the present invention has been shown and described with respectto its preferred embodiments and in the examples, it will be understoodby those skilled in the art that other changes, modifications, additionsand omissions may be made without departing from the substance and thescope of the present invention as defined by the attached claims.

1-30. (canceled)
 31. An electrically conductive shaped articlecomprising a polymer resin and conductive fillers, wherein the polymerresin is a polymer blend comprising (1) from about 10 to 10 wt % of agrafted polyolefin or a blend of grafted polyolefins and (2) from 0 toabout 90 wt % of at least one other thermo plastic polymer having amelting point below 280° C.
 32. The electrically conductive shapedarticle of claim 31 wherein the polymer blend comprises from 50 to 100wt % of a grafted polyolefin or a blend of grafted polyolefins, and from0 to 50 wt % of at least one thermoplastic polymer having a meltingpoint below 280° C.
 33. The electrically conductive shaped article ofclaim 31, wherein the grafted polyolefin is a grafted polypropylene. 34.The electrically conductive shaped article of claim 33, wherein thegrafted polypropylene is maleic anhydride grafted polypropylene.
 35. Theelectrically conductive shaped article of claim 31, wherein the graftedpolyolefin contains from about 0.05 wt % to about 10 wt % ofethylenically unsaturated carboxylic acid or its derivatives graftedonto the grafted polyolefin.
 36. The electrically conductive shapedarticle of claim 35 wherein the grafted polyolefin contains from 0.05 to5 wt % of ethylenically unsaturated carboxylic acid or its derivativesgrafted onto the grafted polyolefin.
 37. The electrically conductiveshaped article of any one of claim 31 comprising from about 10 wt % toabout 50 wt % of the polymer resin and from about 50 wt % to about 90 wt% of the conductive fillers.
 38. The electrically conductive shapedarticle of claim 33, wherein the grafted polypropylene comprises agrafted polypropylene homopolymer, grafted propylene copolymers ormixtures thereof.
 39. The electrically conductive shaped article ofclaim 31, wherein the conductive fillers are selected from carbonfillers, graphite fillers, metallic fillers, inherent conductivepolymers and mixtures thereof, and the conductive fillers are in theshape of spherical or irregular particles, fibers, powders, flakes or amixture thereof.
 40. A conductive flow field separator plate for use ina polymer electrolyte membrane fuel cell comprising the electricallyconductive shaped article of claim
 31. 41. The conductive flow fieldseparator plate of claim 40, wherein the grafted polyolefin containsfrom about 0.05 wt % to about 10 wt % of ethylenically unsaturatedcarboxylic acid or its derivatives grafted onto the grafted polyolefin.42. The conductive flow field separator plate of claim 40, wherein thegrafted polyolefin is maleic anhydride grafted polypropylene.
 43. Theconductive flow field separator plate of claim 40 comprising from about10 wt % to about 50 wt % of the polymer resin and from about 50 wt % toabout 90 wt % of the conductive fillers.
 44. The conductive flow fieldseparator plate of claim 42, wherein the maleic anhydride graftedpolypropylene has a resin base of polypropylene homopolymer, a copolymerof propylene with other olefinic monomers or a mixture thereof.
 45. Theconductive flow field separator plate of claim 40 wherein the conductivefillers are selected from carbon fillers, graphite fillers, metallicfillers, inherent conductive polymers and mixtures thereof, and theconductive fillers are in the shape of spherical or irregular particles,fibers, powders, flakes or a mixture thereof.
 46. The conductive flowfield separator plate of claim 42, having a volume resistivity of notmore than about 0.1 ohm.cm and a flexural strength of not less thanabout 3000 Psi.
 47. A method of making a conductive flow field separatorplate comprising the steps of: (a) mixing a polymer resin withconductive fillers to form a conductive blend, wherein the polymer resinis a polymer blend comprising (1) from about 10 to 100 wt % of a graftedpolyolefin or a blend of grafted polyolefins and (2) from 0 to about 90wt % of at least one other thermoplastic polymer having a melting pointbelow 280° C.; and (b) molding the conductive blend to form theconductive flow field separator plate.
 48. The method of claim 47,wherein the grafted polyolefin comprises from about 0.05 wt % to about10 wt % of ethylenically unsaturated carboxylic acid or its derivativesgrafted onto the grafted polyolefin.
 49. The method of claim 47, whereinthe grafted polyolefin is maleic anhydride grafted polypropylene. 50.The method of any one of claims 47, comprising from about 10 wt % toabout 50 wt %, of the polymer resin and from about 50 wt % to about 90wt %, of the conductive fillers.
 51. The method of claim 49, wherein thegrafted polyolefin has a resin base of a polypropylene homopolymer, acopolymer of propylene with other olefinic monomers or a mixturethereof.
 52. The method of claim 47, wherein the conductive fillers areselected from carbon fillers, graphite fillers, metallic fillers,inherent conductive polymers and mixtures thereof, and the conductivefillers are in the shape of spherical or irregular particles, fibers,powders, flakes or a mixture thereof.
 53. The method of claim 47,wherein the separator plate has a volume resistivity of not more thanabout 0.1 ohm.cm and a flexural strength of not less than about 3000Psi.
 54. A process for making a conductive flow field separator platefor use in polymer electrolyte membrane fuel cells comprising the stepsof: (a) feeding a mixture of a polymer resin and conductive fillers intoan injection molding machine, wherein the polymer resin is a polymerblend comprising (1) from about 10 to 100 wt % of a grafted polyolefinor a blend of grafted polyolefins and (2) from 0 to about 90 wt % of atleast one other thermoplastic polymer having a melting point below 280°C., (b) plasticising the mixture at a temperature above the meltingpoint of the polymer resin to form a melt, (c) injecting the melt into amold, (d) allowing the melt to cure in the mold to form the conductiveflow field separator plate, and (e) removing the conductive flow fieldseparator plate from the mold.
 55. The process of claim 54, wherein instep (c), the mold is closed.
 56. The process of claim 54, wherein instep (c), the mold is partially opened, and comprising the further stepof closing the mold completely and then compressing the melt.